A Filter is a feature in Drupal that allows users to modify the text format of a web page. Filters are used to convert text from one format to another, such as from plain text to HTML, or from HTML to plain text. Filters can also be used to add special features to text, such as adding links, images, or other media. Filters are applied to content when it is displayed on a web page, and can be configured by the user or administrator.
Filters are managed in the Text Formats section of the Drupal administrative interface. Here, users can create and configure text formats, and assign filters to them. Each text format can have multiple filters, and each filter can be configured with different settings. For example, a filter may be configured to automatically convert URLs to links, or to add a specific style to text.
Filters are an important part of Drupal, as they allow users to easily modify the appearance and content of web pages. By using filters, users can create unique and interesting content without having to manually edit HTML or other code. Filters also provide a layer of security, as they can be used to prevent malicious code from being inserted into web pages.